The structure of a traditional AC-DC switching power supply integrated chip is shown in FIG. 1, wherein the start-up circuit 101 and the PWM (Pulse Width Modulation) circuit 102 are integrated together as the control circuit 103, and the power switching transistor acts as the output stage. When the chip is operating, the control circuit outputs driving signals to control the power switching transistor to be in a conducting state or a non-conducting state, and the current of the power switching transistor is sampled through a resistor and is fed back to the control circuit.
In recent years, along with the continuous development of the switching power supply integrated circuit, people are paying more and more attention to high efficiency and low production cost of chips, therefore there is a need to design an advanced semiconductor device.